Evolution of the Earths s Atmosphere 61 



It must be pointed out that the problem of the formation and migration of 

 gases in very deep zones of the Earth is extremely compHcated. It has been 

 suggested that at very high pressure, processes of decomposition of various 

 compounds may take place, and that these processes lead to a diminution in 

 total volume. 



It has been calculated by Parson that, at a pressure of 570,000 kg/cm^, Fe203 

 will dissociate, giving off oxygen. This could occur at a depth of about 1400 km 

 from the surface of the Earth. The later fate of the oxygen thus liberated, and 

 the possibility of its migration to the superficial parts of the terrestrial globe, 

 involve the consideration of many properties of matter at high pressure which 

 are as yet obscure, owing to the subject having been little studied. 



Thus, the evaporation of condensed gases and chemical processes which took 

 place in the prebiogenic stages of the existence of the Earth provided for the 

 appearance in the atmosphere, in the first place, of CO, CH4 and N2 as well as 

 the rare gases (Ne, A, Kr, Xe). At the same time, radiochemical processes led 

 to the appearance in the atmosphere of N2, H2, CO, CH4, NH3 and N2O at 

 temperatures which were still low. The presence of all these gases, in addition 

 to the remains of the original hydrogen, gave rise to reducing conditions on the 

 surface of the Earth. Synthesis of ammonia could have taken place at high pres- 

 sures. Later on, as the temperature rose, there was a greater accession of CO2 

 and O2 to the atmosphere, gases dissolved in the water, NH3 and H2S reacted 

 with other substances and hydrogen was dissipated. All this led to a gradual 

 change from reducing to oxidizing conditions. 



The oxygen, which was being liberated as a result of radiochemical reactions, 

 would seem to have migrated within the crust of the Earth towards its more super- 

 ficial parts (towards a place where the pressure was lower), oxidizing various sub- 

 stances on its way. Such oxygen as managed to reach the atmosphere came into 

 contact with the superficial layers of the crust of the Earth and oxidized them. 

 Later on, the appearance of O2 in the biogenic stage markedly accentuated this 

 oxidative process. Under present-day conditions, therefore, the superficial layers 

 of the crust of the Earth are more highly saturated with oxygen in the form of 

 its various compounds than are the formations which lie more deeply. Not until 

 there had been a considerable degree of oxidation of the material of the crust of 

 the Earth could some of the oxygen, so to speak, force its way out into the 

 atmosphere. In other words, the oxygen which was first formed did not reach 

 the atmosphere and this remained in a reducing state. 



These conditions were suitable for the formation of those compounds which, 

 in the later development of matter, served for the building of living material. 

 A. I. Oparin and other workers [3, 4] have discussed the possibility of the 

 formation of these original substances by abiogenic means. The formation of 

 amino acids by the action of electric discharges on a mixture of CH4 (or CO), 

 H2, H2O and NH3 has been confirmed by the experiments of S. Miller [19]. 

 One may therefore take it for granted that such organic compounds could have 

 been formed as a result of radiochemical reactions. 



The appearance of Hving organisms on the Earth had a great influence on the 

 composition of the atmosphere. The development of living organisms, which 



